The invention relates to a process for the production with continuous supply or fed batch of a sophorolipid composition, incorporating a major part of at least partly acetylated acids and the thus obtained sophorolipid composition.
It is stated in U.S. Pat. Nos. 3,205,150 and 3,312,684 that a quantity of sophorolipids was produced by a fermentation process using a culture of Torulopsis bombicola, a strain presently classified as Candida bombicola. The prior art is also described in U.S. Pat. No. 3,445,337 and in Journal of the American Oil Chemistry Society, vol.65, no.9, September 1988, pp.1460-1466.
French patent application 2670798 also describes a process for the production of sophorolipids by fermentation with continuous supply or fed batch of esters of fatty acids or oils.
The sophorolipids obtained are considered as being a mixture of compounds represented by formulas (1) and (2), formula (1) representing the acid form and formula (2) the lactone form: ##STR1##
In these formulas, R.sup.1 represents hydrogen or an acetyl group and R.sup.2 hydrogen or an alkyl radical having 1 to 9 carbon atoms, when R.sup.3 is a saturated hydrocarbon radical with 7 to 16 carbon atoms, or R.sup.2 represents hydrogen or a methyl group, when R.sup.3 is an unsaturated hydrocarbon radical with 13 to 17 carbon atoms.
Hitherto the preparation processes for products describe numerous homologues and the separation of one of the main forms (acid or lactone) e.g. requires extractions by alcohol (EP-B-209783), which are both long and expensive. Moreover, extraction by a specific solvent does not always give good results, because the solubility of all the homologues in a solvent can differ significantly, which affects the quality of the products obtained.
In addition, methanolysis reactions in the presence of an acid catalyst do not give better results and what is frequently obtained is a mixture of deacetylated esters or acids. The prior art (U.S. Pat. No. 4,197,166) also points out that it is extremely difficult to prepare by fermentation a desired product having a given homologue ratio.
Finally, it is known that the acetyl bonds in sophorolipids are chemically unstable and are very easily hydrolyzed by heating or prolonged storage close to neutrality or even at ambient temperature under slightly alkaline conditions, which leads to the obtaining of the completely deacetylated acid form. It is therefore extremely difficult by fermentation or chemistry to obtain a single product and a fortiori an acetylated product.
Moreover, in petroleum applications e.g. linked with the assisted recovery of petroleum, it is necessary to be able to create water-in-oil emulsions and therefore to be able to have emulsifying products which are more hydrophobic than hydrophilic, which cannot be the case of deacetylated acid products.
Therefore there is a demand in the industry for products having a fatty acid function and a saccharide structure with acetylated functions masking the very hydrophilic hydroxyl groups, particularly on products obtained by fermentation and incorporating a saccharide structure such as sophorose.